A cardiac sphincter is a ring of specialized muscle fibers that acts like a valve within the digestive system. This muscular band regulates the movement of food, ensuring it travels in the correct direction through the digestive tract.
Where the Cardiac Sphincter Is Located
The cardiac sphincter, more commonly known as the lower esophageal sphincter (LES), is a muscular ring at the end of the esophagus, where it meets the stomach. This position places it just below the diaphragm. Its name, “cardiac,” comes from its close anatomical proximity to the heart, not because it has any direct function related to the heart itself.
How the Cardiac Sphincter Works
The primary function of the lower esophageal sphincter is to act as a one-way gate, allowing swallowed food to enter the stomach while preventing its return to the esophagus. Under normal conditions, this sphincter remains tightly contracted.
When a person swallows, a wave of muscle contractions, known as peristalsis, travels down the esophagus. Just ahead of this wave, the LES relaxes to allow the food bolus to pass into the stomach. Once the food has entered the stomach, the sphincter contracts and closes. This closing action creates a barrier that keeps the stomach’s highly acidic contents and digestive enzymes from flowing backward into the more sensitive esophageal lining.
When the Cardiac Sphincter Doesn’t Work Properly
When the lower esophageal sphincter malfunctions, it can lead to health issues. A common problem occurs when the sphincter weakens or relaxes at inappropriate times, allowing stomach acid and digestive juices to reflux into the esophagus. This backward flow causes a burning sensation behind the breastbone, commonly known as heartburn. If this acid reflux happens frequently, it can develop into gastroesophageal reflux disease (GERD).
Chronic exposure to stomach acid can irritate the esophageal lining, leading to inflammation called esophagitis, and potentially more severe complications such as Barrett’s esophagus, which increases the risk of esophageal cancer. Several factors can contribute to a weakened or improperly functioning LES. These include conditions like hiatal hernia, where part of the stomach pushes up through the diaphragm, displacing the sphincter and reducing its effectiveness. Other contributing factors can be pregnancy, obesity, smoking, and certain medications, all of which can either increase abdominal pressure or directly relax the sphincter. In rare cases, the LES may fail to relax properly, a condition called achalasia, which prevents food from entering the stomach and can lead to food accumulation in the esophagus.